The beavers in Canada’s Wood Buffalo National Park have been hard at work for decades, and their tree-chomping labor has paid off. The furry architects have created the largest beaver dam in the world.

The dam, which is about a half a mile long, is so massive it even shows up on satellite images. It remained hidden within the Alberta wilderness until 2007, when a researcher spotted it while looking at Google Earth. The beavers are currently building new dams nearby, which when joined with the main structure could add over 300 more feet to its length.

Beavers are one of the few species capable of creating structures that are significant enough to be seen from space. The toothy critters are remarkable environmental engineers. Their dams reroute streams and even alter entire ecosystems. These creations, which are built to last, are barriers that form ponds, which act like defensive moats to protect them from predators like wolves and bears.

It’s likely the beavers began working on the Alberta dam sometime in the 1970s, making it a multi-generation architectural endeavor. The hodgepodge of mud, branches, stones, and twigs is cloaked in a layer of grass, meaning it’s been there for a while. The dam stretches across a remote wetland area, which provides the creatures with both plenty of fresh water and bountiful building materials. The isolated location makes it difficult for any curious human to reach and disturb the site.

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